DEVELOPMENT 



421 



grasshopper develops from the young larva to the 

 winged adult without changing its mode of life. In 

 the development of the common crab, so different is 

 the outward form of the newly hatched embryo from 

 that of the adult, that the former has been described as 

 a distinct species. 



The most remarkable example of metamorphosis 

 among vertebrates is furnished by the amphibians. A 



FIG. 370. Metamorphosis of the Newt. 



tadpole the larva of a frog- has a tail, but no legs; 

 gills, instead of lungs ; a heart precisely like that of the 

 fish ; a horny beak for eating vegetable food, and a 

 spiral intestine to digest it. As it matures, the hinder 

 legs show themselves, then the front pair; the beak 

 falls off ; the tail and gills waste away ; lungs are 

 formed ; the digestive apparatus is changed to suit an 

 animal diet; the heart is altered to the reptilian type 

 by the addition of another auricle ; in fact, skin, mus- 

 cles, nerves, bones, and blood vessels vanish, being ab- 



